The objective of this research project is to determine those factors which participate in sustaining elevated blood pressure in the chronic phase of renovascular hypertension. We are particularly interested in the phase of hypertension which does not respond to angiotensin antagonists but does respond to removal of the renal artery clip with a significant decrease in blood pressure. The purpose of this proposal is to identify factors other than the renin-angiotensin system (such as sodium and hypothetical unknown factors) which participate in the pathogenesis of chronic two-kidney renal hypertension (one kidney clipped, contralateral untouched) and one-kidney renal hypertension (one kidney clipped, contralateral removed). We also plan to study the cause of residual hypertension after unclipping the renal artery in chronic (6 months after clipping) two-kidney renal hypertension. In this situation, it has been observed that the blood pressure decreases after unclipping; however, in a significant proportion of animals, a residual hypertension persists, which is abolished by removing the contralateral kidney. Similar results have been observed in humans. These studies are important, not only because they could help to explain the pathogenesis of chronic renovascular hypertension, but also because they may increase our understanding of more general mechanisms which participate in maintaining elevated blood pressure. This, in turn, could help to elucidate the pathogenesis of other types of hypertension.